The invention relates to apparatus for the optional retention of the two reciprocatingly driven control elements of the shed forming arrangement associated with a loom.
A known shed-forming arrangement having such apparatus is disclosed in Swiss Patent Specification No. 543 127. Each such apparatus is associated with a control element and comprises an electromagnet, which is energized in accordance with a control programme, a retaining element, which is pivotable about a stationary shaft and constructed as the armature of the electromagnet, and an actuating device with two actuating elements and with a control mechanism which is actuated in accordance with the motion of the control element at the operating timing of the loom, in order to actuate the retaining element.
The armature is placed upon the electromagnet by the control mechanism, actuated at the timing of the loom, and by an actuating element. If the electromagnet is energized, the armature is held and the retaining element does not influence the reciprocatingly moving control element until the armature is drawn off the electromagnet by the control mechanism and by the second actuating element, whereupon the reciprocating control element is retained. If the electromagnet is not energized, the armature is directly pulled off the electromagnet by a spring.
The retaining element therefor performs a reciprocating motion which is defined by the operating timing of the loom, i.e., it operates in a cycle defined by the control mechanism and by the two actuating elements.
The reciprocating motion must be performed within a time which depends on the clearance that occurs between the hook portions of the retaining element and of the control element in its lowest position. In other words, the velocity of the control element is dependent on the time of one reciprocating motion of the retaining element. The operating speed of the loom is thus restricted, which is a disadvantage.
Another disadvantage is due to the fact that relatively large accelerating forces occur due to the rapid reciprocating motion of the retaining element. As a result, both the armature and the electromagnet can be damaged, on the one hand due to the severe impact of the armature so that the loom is subject to malfunctioning, and on the other hand it is necessary for a heavier construction to be adopted for the loom.
The contact time for the armature is very short owing to the rapid reciprocating motion of the retaining element. The magnetic field to be produced by the electromagnet must be correspondingly powerful, so that the electromagnet must be designed for a higher power, which is also a disadvantage.
It is here that the invention provides a remedy. The invention solves the problem of providing an apparatus of the initially mentioned kind, in which the actuating element is brought into contact with, and out of contact from, the control device, independently of the control element cycle, and is able to scan the magnetic field and is displaced in the direction of the retaining element only when the control device is not energized.
The advantages thus achieved are that the time for scanning the magnetic field and preparation of the actuating element for pivoting is independent of the control element cycle so that practically an entire control element cycle is available for scanning the magnetic field and that the retaining element is moved in only one direction during the period of time which depends on the clearance. The accelerating forces are thus reduced or the velocity of the actuating elements or of the control elements can be increased.
In one exemplied embodiment of the invention, the control apparatus contains two electromagnets and the driving mechanism comprises two shafts each of which is associated with a stationary shaft. The retaining element is retained on the one hand on the shaft and on the other hand is in engagement with the shaft so that the actuating element can be brought into contact with or out of contact from the electromagnet by means of the shaft.
This offers the advantage that the retaining element need only perform a retaining function and can thus be made less strong while the low accelerating forces and the elasticity of the actuating element substantially avoid damage thereof or of the electromagnet.
In a preferred embodiment of the invention the control device comprises an electromagnet and the driving mechanism only one shaft which is associated with two stationary shafts. Two actuating elements are provided symmetrically with respect to the shaft and are retained on the one hand on one spindle and on the other hand are in engagement with the shaft. The actuating elements are alternately brought into contact with, and out of contact from, the electromagnet and each is displaced when the electromagnet is not energized.
This embodiment offers the advantage that only one electromagnet and one shaft is required so that the apparatus is substantially simplified and power consumption of the apparatus can be substantially reduced.
It is also advantageous if the actuating elements are components of U-shaped configuration, because these components can merely be slid on to the stationary axle so that installation and more particularly repair can be greatly simplified.
Another advantage is due to the fact that the retaining element is a leaf spring so that the mass of the retaining element is greatly reduced and accelerating forces become correspondingly small.